In military ordnance arts, carriers for projectiles, known as sabots, have been used to facilitate the use of a variety of munitions while engaging in military operations.
In general, a sabot is a lightweight carrier for a projectile that permits the firing of a variety of projectiles of a smaller caliber within a larger caliber weapon. The word sabot is derived form the French word cabot, which means, "shoe." Because a sabot fits around the projectile in a manner similar to the way a cabot, or "shoe," slips onto a persons foot, the name has been applied to all such projectile carriers.
A sabot provides structured support to a flight projectile within a gun tube under extremely high loads. Without adequate support from a sabot, a projectile may break up into many pieces when fired.
A sabot fills the bore of the gun tube while encasing the projectile to permit uniform and smooth firing of the weapon. The projectile is centrally located within the sabot that is generally radially symmetrical. After firing, the sabot and projectile clear the bore of the gun tube and the sabot is normally discarded some distance from the gun tube while the projectile continues toward the target.
One method for discarding a sabot is to form a scoop onto the sabot. After the sabot and projectile clear the weapon bore, the scoop gathers, or "scoops," air particles as it is moving forward. The air pressure on the front scoop lifts the sabot from the projectile and thus the sabot is removed from the projectile in flight, allowing the projectile to continue towards its target.
Additionally, sabots are generally made in three symmetrical segments to facilitate smooth discard upon exit from the gun. Typically, each segment, or petal, spans 120 degrees of the front circumference of the intact sabot. Each petal's scoop portion is still expansive enough, at 120-degrees, to serve its purpose of driving the petal away from the projectile. The three segment design allows sabot petals to discard from the projectile quickly, as opposed to, for example, a design where an intact sabot gradually slips off of the projectile. The overall advantage of a three petal sabot design is that the sabot is released more quickly, thereby reducing parasitic weight and increasing accuracy.
It is desirable to make sabots lightweight to increase the muzzle velocity of projectile at exit. At the same time, the sabot must maintain its rigidity during operation. For example, inside the bore of the weapon the sabot must stay rigid to allow smooth firing and accurate targeting. Further, once outside the bore of the weapon, the sabot must maintain rigidity in order to scoop air particles efficiently, discard its three petals, and allow acceptable projectile dispersion on the target.
The weight of sabots has been reduced considerably through the use of continuous fiber composite material. Generally, such composite sabots are mixtures of fibers and epoxy combined in a chemical molding process. The weight reductions are made possible by aligning the fibers in the longitudinal/radial plane of the sabot which matches the load directions generated during the projectile travel down the weapon bore.
Unfortunately, during sabot discard, significant circumferential, or hoop, tensile loads are created. Since no fibers are oriented in the circumferential, or hoop, direction in known lightweight sabot designs, the sabot splits along the longitudinal/radial plane typically near the middle of the sabot scoop. Compounding the problem, a faulty molding process may leave air voids in the structure of the sabot, which increases the probability that a sabot petal of conventional design will split into more than two pieces.
Consequently, composite sabot petals of conventional design usually split in the middle from the high hoop stresses generated during discard. Thus, a 120-degree petal may split into two 60-degree segments due to the lack of strength in the circumferential direction of the sabot. This could result in asymmetric discard, where the petals are released at different times, and poor projectile dispersion on the target. It also has been found that a 60-degree segment of split sabot petal is more likely to fail in the scoop or break in the saddle compared to 120-degree intact sabot petal. Further, such splits occur with considerable variation in the location and time of splitting. Thus, compensation for the sabot failure using targeting adjustments is very difficult.
Previous attempts to stop the splitting of composite sabots involved filament wrapping. In this process, the entire assembled projectiles are wrapped with filaments, and then the filament wrap is slit along the seams between the sabot petals. However, this process is unwieldy and expensive from a manufacturing standpoint. Further, filament wrapping is known to be ineffective for preventing all sabot splitting problems.